1. Field of the Invention
The present invention relates to a thin film magnetic head including a magnetoresistive element and a method of manufacturing the same, and also relates to a magnetic head slider, head gimbal assembly, head arm assembly and magnetic disk device including the thin film magnetic head.
2. Description of the Related Art
A thin film magnetic head, which includes a magnetoresistive element (MR element) exhibiting the magnetoresistive effect (MR effect), is widely used for reading data written on magnetic recording media such as a hard disk. Recently, a thin film magnetic head which includes a giant magnetoresistive element (GMR element) exhibiting the giant magnetoresistive (GMR) effect is generally used because of highly-progressed recording density of the magnetic recording medium. Examples of such GMR element include a spin valve GMR element (SV-GMR element).
This SV-GMR element is configured in such a manner that a magnetic layer in which its magnetization direction is fixed in a given direction (magnetically pinned layer) and a magnetic layer in which its magnetization direction is varied in accordance with an external signal magnetic field applied from outside (magnetically free layer) are stacked via a nonmagnetic interlayer. In particular, those configured to make a read current pass in a direction along a stacking plane of the element during a reading operation is called CIP-GMR element (Current in Plane GMR element). Further, a thin film magnetic head including the CIP-GMR element is called CIP-GMR head. In this case, electric resistance (namely, voltage) is varied when the read current is applied in accordance with a relative angle between the magnetization directions of the two magnetic layers (the magnetically pinned layer and the magnetically free layer).
Recently, in response to the further improvement in the recording density, development of a CPP (Current Perpendicular to the Plane)-GMR head, which includes a CPP-GMR element in which the read current flows during the reading operation in a direction orthogonal to the staking plane, has been advanced (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-329905). Such CPP-GMR head generally includes a GMR element, a pair of magnetic domain controlling layers that are arranged to face each other in a track-width direction with the GMR element in between via an insulating layer, and a lower electrode and an upper electrode that are arranged to face each other with the GMR element and the pair of magnetic domain controlling layers in between in the stacking direction. The upper and lower electrodes also serve as upper and bottom shielding layers. Such CPP-GMR head recognizes advantages in that high power is available when reducing the dimension in a read track width direction compared with the CIP-GMR head. Namely, in the CIP-GMR head, since the read current flows along the in-plane direction, the dimensional reduction in the read track width direction results in the narrowing of magnetic sensitive area through which the read current passes, thereby decreasing the amount of voltage changes. On the other hand, since the read current passes in the stacking direction in the CPP-GMR head, the dimensional reduction in the read track width direction does not affect the amount of voltage changes. For this reason, the CPP-GMR head is advantageous compared with the CIP-GMR head in terms of track density, which is expressed with TPI (number of tracks per inch). What is more, since insulating layers are omitted between the CPP-GMR element and upper/lower shielding films, that allows the reduction, by the thickness of the omitted layers, of the linear recording density, which is expressed with BPI (Bit Per Inch), as compared with the CIP-GMR head.
There is also a tunnel MR element (TMR element) which is configured similar to the CPP-GMR element in that the read current flows in a direction orthogonal to the in-plane direction. This TMR element further includes an ultra-thin insulating layer called a tunnel barrier layer so as to obtain much higher resistance change ratio than that of the above-mentioned CPP-GMR element. For this reason, the thin film magnetic head including the TMR element (TMR head) is highly expected to respond to the further improvement in the recording density.
Recently, a magnetic head, which includes a CPP-MR element in which two magnetically free layers are stacked with a nonmagnetic interlayer in between, has been proposed, as shown in U.S. Pat. No. 7,035,062. In this CPP-MR element, the two magnetically free layers are subjected to exchange coupling by what is called RKKY interaction via the nonmagnetic interlayer. In this magnetic head, a hard magnet layer is arranged at the rear of the CPP-MR element (on a side opposite to an air bearing surface) so that a bias magnetic field may be applied in the direction orthogonal to the air bearing surface. Because of this bias magnetic field applied, magnetization directions of the two magnetically free layers are relatively fixed to each other at a certain relative angle. If a signal magnetic field (external magnetic field) is given from a magnetic recording medium under this condition, the relative angle of the two magnetically free layers is changed and there appears a change in the electric resistance of sensing current. Such CPP-MR element needs no pinned layer or pinning layer because of its configuration. Accordingly, it is easily thin-shaped, and what is more, the read gap thereof may be narrowed so as to improve the read resolution.
By the way, in any of the above-mentioned various types of MR elements, the height or the dimensions from the front (edge portion exposed to an air bearing surface) to the back (edge portion on a side opposite to the air bearing surface) of the MR element is an important factor affecting the reading performance of a thin film magnetic head. Such height in the MR element is called MR height. To reduce errors in manufacturing the MR height, various techniques have been proposed with regard to the method of manufacturing the MR elements. For example, Japanese Patent Publication No. 2005-294610 discloses a method in which a resistance element (wrapping guide) is disposed side by side with an MR film at a given position, variation of the resistance of the resistance element is observed while polishing both of the MR film and the resistance element simultaneously and stop polishing when the resistance becomes a fixed value. In particular, here, since a photoresist pattern for determining the previous dimensions of the MR element and the resistance element before the polishing operation is formed in a lump-sum formation, more accurate MR height is available.